Hydrostatic bearing

ABSTRACT

In a hydrostatic bearing comprising a bearing unit having a friction face, bearing pockets in the friction face, means for feeding pressurized liquid into the pockets and a capillary associated with each pocket to act as a hydraulic resistance: the improvement of a common feed passage for a plurality of the bearing pockets, an individual feed duct leading into each of the bearing pockets and the capillary associated with each bearing pocket is in the form of a capillary tube have two ends, one end being sealingly secured in the feed duct leading to that bearing pocket and the other end extending into the common feed passage.

United States Patent Beisemann [45'] Mar. 21, 1972 54] 'HYDROSTATICBEARING 3,062,046 11/1962 Evans .l ..308/5 [72] Inventor: 231:2Belsemann, Monchengladbach, Ger- Primary Examiner Manin P schwadmn yAssistant Examiner-Frank Susko [73] Assignee: P. Konings'Machinefabriek, ljzer-en Attorney-Herbert E. Kidder Metaalgieterij N.V.

221 Filed: June 10, 1970 [57] ABSTRACT [211 App] 45 033 In a hydrostaticbearing comprising a bearing unit having a friction face, bearingpockets in the friction face, means for feeding pressurized liquid intothe pockets and a capillary as- [30] Foreign Application Priority Datasociated with each pocket to act as a hydraulic resistance: the June 141969 Germany ..P 19 30 376.5 impmvemem a Passage pluraliy Oct. 22 1969Germany "p 19 5 3 1603 bearing pockets, an individual feed duct leadinginto each of the bearing pockets and the capillary associated with each52 vs. c1 ..30s/9 bearing Pocket is in the form of a capillary tube havetwo ends. [5]] InLCL I t 1131 17/1 one end being sealingly secured inthe feed duct leading to [58] Field of Search ..308/9, 122, 5 that ringpocket and the other end extending into the com- 7 mon feed passage.

R f e Cit d [56] e ereinc s e 11 Claims, 9 Drawing Figures UNITED STATESPATENTS 2,049,343 7/1936 Warren ..308/9 Patented March 21,1972 3,650,580

INVENTOR Patented March 21, 1972 4 Sheets-Sheet 2 I N V EN T0 R.

HE/NZ BE/SEMAA/N Patented March 21, 1972 3,650,580

4 Sheets-Sheet 5 INVEN TOR.

HEM/Z BE/SEMflN/V HYDROSTATIC BEARING The invention relates tohydrostatic bearings comprising bearing pockets formed in frictionsurface of the bearing unit and arranged to receive oil or other liquidfed under pressure through capillary ducts.

Hydrostatic bearings are known in the form of radial and axial bearingsas well as in the form of machine saddle slideways and hydrostatic nutsfor lead screws, and they are particularly used in the construction ofmachine tools. Hydrostatic bearings operate in such manner that apressure-resistant film of oil or other liquid is built up between thecontact surfaces of relatively displaceable parts, which film is alsomaintained under fluctuations of load, to prevent direct contact betweenthe two bearing surfaces.

For acceptable operation of hydrostatic bearings, it has been found tobe appropriate for each bearing pocket to be supplied from a separatepump, or for a shared pump to be incorporated for all or a group ofbearing pockets, in which case each individual bearing pocket ispreceded by a hydraulic resistance whereby a fall in the pressure in onebearing pocket does not adversely affect the feed to the others fed fromthe same pump.

Restrictors or capillaries may be considered as possible hydraulicresistances. Restrictors have been found to be disadvantageous however.They represent a hydraulic resistance which is independent of viscosity,whereas the hydrostatic hearing has a hydraulic resistance which isdependent on viscosity in consequence of laminar flow conditions. Sincethe bearing is arranged in series with the restrictor, the ratio betweenthe series resistance represented by the restrictor and the bearingresistance, which ratio is very important for the properties of thehydrostatic bearing, also varies during temperature fluctuations andfluctuations in the viscosity of the oil.

This disadvantage is eliminated by application of capillaries as seriesresistances, since these equally have a resistance characteristicdependent on viscosity. Accordingly, the ratio between the resistancesalways remains constant under application of capillaries as series orbarrier resistances, even with fluctuating viscosity of the oil.

Another reason for the frequent use of capillaries as series resistancesresides in that the aperture diameter of the capillaries issubstantially greater by comparison with restrictions of similarhydrostatic series resistance value, thereby reducing the riskofblockage by solid material.

However, the known hydrostatic bearings using capillaries have thedisadvantage that a connector with a capillary tube must be fitted foreach bearing pocket. To this end, the capillary tubes must be adaptedprecisely in respect of their length and diameter to the specialconditions applicable to each bearing, which requires voluminouscalculations for each kind and type of bearing. Also, the labor cost forassembly is considerable in the case ofknown hydrostatic bearings, sincefour connectors are needed for a bearing comprising four bearing pocketsfor example.

The invention is based on the problem of simplifying the structuralarrangement and assembling operation of hydrostatic bearings. To thisend, the hydrostatic bearings are to be formed in such manner that theymay be employed as readymade fitting elements, without requiring anydrilling in the housing for the fitting of the pressurized feed passage.

Accordingly, the invention consists in a hydrostatic bearing comprisingbearing pockets formed in a friction face of a bearing unit and arrangedto receive pressurized oil or other liquid through capillaries, in whichthe capillaries consist of capillary tubes each having one end sealinglyarranged in a bearing pocket feed duct and the other end leading into acommon pressurized feed passage.

Provision may be made for the other extremities of the capillary tubesto project in a non-fastened manner into the pressurized feed passage.The entry of pressurized liquid into the capillary tubes thus occurs atthe free extremities. The pressurized liquid then issues from thefastened extremities and flows into the bearing pockets.

Bearing pocket feed tubes may be arranged transversely to the commonpressurized oil feed passage and the capillary tubes conform generallyto the configuration of the pressurized oil feed passage and of thebearing pocket feed tubes.

The fastening of the capillary tubes may be performed by screwing intothe bearing pocket feed tubes or by welding or brazing into counterboresof the bearing pocket feed tubes.

In the case of a radial bearing, provision may be made for thepressurized feed passage to consist of an annular groove surrounded by aring, the ring simultaneously forming the external periphery of theradial bearing. A particularly simple method of assembly of thehydrostatic bearing is accomplished by this measure, since the annulargroove is formed first, after which the bearing pocket feed passages areformed, for example in the form of drillings leading to the bearingpockets, after which the capillary tubes are fastened, and the annulargroove can finally be closed off, possibly with interposition of seals,by means of the ring, which may be shrunk on.

In the case of hydrostatic bearings, it is considered to bedisadvantageous moreover, that with a hydrostatic bearing having severalindividual connectors for the supply of pressurized oil, the rise intemperature caused by pressure drop in the capillaries results in areduction of the viscosity of the pressurized oil. This effect cannot becompletely prevented even by inclusion of a cooling system in thepressurized oil supply. Since a constant viscosity is taken as a basisin the calculations affecting hydrostatic bearings, greater deviationsfrom the theoretically calculated bearing values intervene in practicalapplication. If a cooling system is not incorporated, pressurized oilwhich is already warm is fed to the bearing, which causes a furtherincrease in the deviations occuring in practice. Although precooling ofthe pressurized oil thus cannot in any event prevent the temperaturerise occurring in the capillaries, an excessive degree of precoolingmoreover results in the forming of dew at appropriate externaltemperatures.

The actual bearings, that is to say the bearing surfaces of hydrostaticbearings sliding on each other through an oil film, cannot be cooledeither in sufficient degree in the present forms of bearing. Althoughforms of bearings are known in which the bores in the housings receivingthe bearings have grooves wrought in them which are sealed by thebearing itself, and a part of the heat generated within the bearing iscarried off if a coolant is caused to circulate through these grooves,it is disadvantageous in this connection that the machining of groovesinto the high precision bore produced is very costly, and sealingproblems arise in this connection.

To eliminate the problem arising in respect of cooling, it is furtherproposed to provide a possibility of cooling the capillaries as well asthe actual bearing points.

This is accomplished by the fact that another connector for drawing offpressurized oil not required to act on the bearing pockets isincorporated in the hydrostatic bearing in addition to the connectorconnected to the pressurized oil feed passage. If a surplus of cooledpressurized oil is fed to the hydrostatic bearing, the surplus portionof the oil flows past the capillaries and back to the oil pump throughthe additional connector. The capillaries are concomitantly cooled alongtheir entire length.

In the case of radial bearings, it is appropriate for the two connectorsto be arranged at opposite sides of the hydrostatic bearing in eachcase. In other forms of bearings, the secondary or additional connectorshould be arranged in such manner that a flow of oil between the twoconnectors flows past all the capillaries.

In this connection it is advantageous for the pressure-limiting valveneeded for the oil supply system to be arranged down stream of theadditional connector. In the known embodiments of hydrostatic bearings,the hydrostatic bearing is down stream of the pressure-limiting valve.

To secure cooling of the actual bearing points, provision may be made toincorporate cooling passages traversed by the flow of pressurized oil inthe direction; of the pressurized oil feed passage. The possibility isconcomitantly available to connect the cooling passages in shunt withthe pressurized oil feed passage. The connection of the cooling passagesmay then be made to the connector for the pressurized oil feed passageand to the connector for drawing off the pressurized oil not needed toact on the bearing pockets.

Alternatively a separate coolant circulation may be incorporated for thecooling passages. Since, in such a case, there is no connection betweenthe oil circuit and the coolant circuit, separate connectors arerequired in each case for the inflow and outflow of the coolant.

It is advantageous that it is possible to eliminate the cooling grooveshitherto required in the reception bores and reception surfaces of gearsand machine saddles, as well as the sealing problems arising.

A closable and externally accessible connector may be incorporated foreach bearing pocket. These connectors serve the purpose of accommodatinga measuring instrument, so that it is possible in this way to measurethe pressure in the individual bearing pockets of the bearing in theassembled condition.

The invention will be further described in various embodiments given byway of example and illustrated in the accompanying drawings, in which:

FIG. 1 is an axial section through a radial hydrostatic bear- FIG. 2 isa section along the line II-II in FIG. 1;

FIG. 3 is a sectional view ofa hydrostatic slideway;

FIG. 4 is a plan view of the structure of FIG. 3;

FIG. 5 is an axial section through a radial hydrostatic bearing with acooling system;

FIG. 6 is a section along line VI-VI in FIG. 5;

FIG. 7 is a section along line VII--VII in FIG. 5;

FIG. 8 is a sectional view of hydrostatic slideway with a coolingsystem; and

FIG. 9 is a plan view of the structure of FIG. 8.

The radial hydrostatic bearing illustrated in FIG. 1 has a cylindricalbearing element 1. On the inner surface are incorporated altogether fourbearing pockets 2 in opposed pairs. On the outer surface, the bearingunit 1 has a flangelike extension 3 at one longitudinal end. Acontinuous annular groove 4 is formed approximately in the middle of thebasic bearing unit I. This annular groove 4 is sealed off by means ofaring 5 which is secured on the outer surface of the bearing unit 1,e.g., by shrink fitting, and with one end bears against the extension 3.Seals 6 are fitted between the bearing unit 1 and the ring 5.

The annular groove 4 is fed with pressurized oil or other liquid from apump which is not shown, through a connector 7 and bores 8 and 9. Adrilling 10 having an end opening towards the annular groove 4 andprovided with a counterbore 11, is provided to carry the oil to eachbearing pocket. Capillary tubes 12 are secured in the drillings 10. Thesecuring is performed either by brazing or welding, or by screwingthreaded ends of the tubes 12 into tapped holes 10, as in FIGS. 1 and 2;the latter securing method being preferable for larger bearings. Thecapillary tubes 12 correspond to the configuration of the pressurizedoil feed passage consisting of the annular groove 4 and the drillings10.

When the annular groove 4 receives pressurized oil, this oil passesthrough the freestanding ends 12a into the capillary tubes 12. Afterappropriate pressure reduction, the pressurized oil passes into thebearing pockets 2 to form a pressure resistant oil film between theradial bearing element 1 and a shaft (not illustrated) present withinthe radial bearing.

FIGS. 3 and 4 show a saddle slideway having a similar structure. Thepressurized oil feed passage is a bore 13, from which drilling 14 leadobliquely outwards to bearing pockets 15. Starting from these bearingpockets, capillary tubes 16 are inserted into the bore 13 and have oneextremity secured in counterbores 17 or in the drillings 14. The otherextremity extends loosely into the bore 13. When the bore 13 forming thecommon pressurized oil feed passage receives pressurized oil from a pump(not shown) through a connector 18, the oil penetrates into thecapillary tubes 16 and after appropriate pressure reduction emerges intothe bearing pockets 15. In these, a pressure resistant oil film is thenformed between the bearing and another plane friction face (not shown).

In the further examples of embodiment illustrated in FIGS. 5 to 9, theparts corresponding to the illustrations in FIGS. 1 to 4 are marked bythe same reference numerals.

In the radial bearing illustrated in FIGS. 5 to 7, several coolingpassages 13a in the form of grooves are formed in the bearing unit 1 inthe direction of the annular groove 4. These grooves 13a are connectedto the connector 7 through drillings 10a and the bore 8. The pressurizedoil not required to act on the bearing pockets 2 enters the coolinggrooves 13a, and emerges again through another connector 7a which issituated opposite the connector 7. To this end, the cooling passages 13aare connected via drilling 10b and a bore with the further connector 7a.The further connector 7a serves the purpose of drawing off thepressurized oil and returning it to the oil pump or to an oil receptionvessel. The connector 7a is followed by a pressure-limiting valve (notshown). The annular groove 4 is also connected to the bore 8a through abore 9a.

A part of the pressurized oil fed to the hydrostatic bearing enters thecooling passages 13a and just like the surplus oil flows off in thepressurized oil feed groove 4 through the connector 7a. Duringthroughflow of the cooled pressurized oil through the pressurized oilfeed passage 4, the capillaries 12 are supplied with oil and aresimultaneously cooled along their entire length. The oil flowing in thecooling passages 13a dissipates the heat generated at the actual bearingpoints and prevents the heat from penetrating outwards into possiblyadjacent walls of gear systems or the like.

The possibility is available moreover to arrange a coolant supply forthe cooling passages 13a separately from the oil circuit. In this case,two further connectors are needed, namely for the coolant inflow and thecoolant outflow. In a system of this kind, the cooling performance isgreater than in the case of the cooling system illustrated in FIG. 6,which is operated in a secondary circuit.

It is apparent from FIG. 7, that each bearing pocket 2 has anotherconnector 20 associated with it, which is closed off in the normal caseby a plug (not shown) and is connected to the bearing pockets 2 throughbores 21 and 22. If the plug is removed and a pressure gauge isconnected instead to the connector 20, it is possible to measure thepocket pressure prevailing in the individual bearing pockets in theassembled condition of the bearing.

The hydrostatic slideway illustrated in FIGS. 8 and 9 has a structuresimilar to the arrangement just described. In this case, the pressurizedoil feed passage consists of a bore 13, from which drillings 14 leadobliquely outwards to bearing pockets 15. Starting from these bearingpockets, capillary tubes 16 are inserted into the bore 13 and have oneend secured in counterbores 17 or in the drillings 14. The other endprojects loosely into the bore 13. When the bore 13 forming the commonpressurized oil feed passage is acted upon by pressurized oil comingfrom a pump (not shown) through a connector 18, the oil enters thefreestanding extremities of the capillary tubes 16 and after appropriatepressure reduction emerges into the bearing pockets 15. In these is thenformed a pressure resistant oil film between the bearing and anotherplane friction surface (not shown).

Opposite to the connector 18, at the other end of the bore 13, isarranged another connector 18a which is followed by a pressure limitingvalve. When a surplus of cooled pressurized oil is fed to the slidewayor to the bore 13, this surplus flows along past the capillaries l6 andcools these along their entire length. Further bores acting as coolingpassages (not shown) and extending parallel to the bore 18 may betraversed in secondary flow for the cooling of cooled pressurized oil.The cooling performance may also be increased by a separate coolingsystem, that is to say without connection between the cooling passagesand the pressurized oil feed passage 13. in this case two furtherconnectors will evidently also be needed, that is to say for the inflowand outflow of the coolant. Each bearing pocket is associated with anexternally accessible connector 19, which is in communication with thebearing pocket 15 through bores a. Normally, the connectors it? areclosed off by a plug (not shown). If the plug is removed, and if apressure gauge is joined to the connector 19 instead, the pocketpressure in each bearing pocket 15 may be read off in the assembledcondition of the slideway.

Various modifications may be made within the scope of the invention.

lclaim:

1. In a hydrostatic bearing comprising a bearing unit having a frictionface, bearing pockets in the friction face, means for feedingpressurized liquid into the pockets, the improvement comprising a commonfeed passage for a plurality of the bearing pockets, an individualfeed'duct leading into each of the bearing pockets, and an elongatedcapillary tube associated with each of said bearing pockets, saidcapillary tubes each having two ends, one end being sealingly secured inthe feed duct leading to that bearing pocket, and the other endextending loosely into said common feed passage for the greater part ofits length, said capillary tubes each providing hydraulic resistance toflow of said liquid into their respective bearing pockets, theresistance characteristic of said capillary tubes being dependent onviscosity.

2. A hydrostatic bearing as claimed in claim l, in which the feed ductsare arranged transversely to the common feed passage and the capillarytubes conform generally in shape to the feed duct and the common feedpassage.

3. A hydrostatic bearing as claimed in claim 1, in which the capillarytubes are threadedly received in the feed ducts.

11. A hydrostatic bearing as claimed in claim 1, comprising counterboresto the feed ducts in which the capillary tubes are welded into thecounterbores.

5. A hydrostatic bearing as claimed in claim 1, comprising counterboresto the feed ducts in which the capillary tubes are brazed into thecounterbores.

16. A hydrostatic bearing as claimed in claim 1, in the form of a radialbearing, in which the bearing unit has an outer face with a groove inthe outer face constituting the common feed passage, and comprising aring forming the outer surface of the bearing and closing the saidgroove.

"7. A hydrostatic bearing as claimed in claim 1, comprising a connectionfor connecting the common feed passage to an external pressure source,and a further connector connected to the common feed passage for drawingoff liquid fed to the common feed passage in excess of that required forfeeding to the bearing pockets.

8. A hydrostatic bearing as claimed in claim 7, in which the connectorand the further connector are arranged in opposition.

9. A hydrostatic hearing as claimed in claim 7, comprising coolingpassages in the bearing unit for carrying pressurized fluid.

it A hydrostatic bearing as claimed in claim 9, in which the coolingpassages are connected in parallel with the common feed passage.

llll. A hydrostatic bearing as claimed in claim 1, comprising a closableand externally accessible connector for each bearing pocket.

1. In a hydrostatic bearing comprising a bearing unit having a frictionface, bearing pockets in the friction face, means for feedingpressurized liquid into the pockets, the improvement comprising a commonfeed passage for a plurality of the bearing pockets, an individual feedduct leading into each of the bearing pockets, and an elongatedcapillary tube associated with each of said bearing pockets, saidcapillary tubes each having two ends, one end being sealingly secured inthe feed duct leading to that bearing pocket, and the other endextending loosely into said common feed passage for the greater part ofits length, said capillary tubes each providing hydraulic resistance toflow of said liquid into their respective bearing pockets, theresistance characteristic of said capillary tubes being dependent onviscosity.
 2. A hydrostatic bearing as claimed in claim 1, in which thefeed ducts are arranged transversely to the common feed passage and thecapillary tubes conform generally in shape to the feed duct and thecommon feed passage.
 3. A hydrostatic bearing as claimed in claim 1, inwhich the capillary tubes are threadedly received in the feed ducts. 4.A hydrostatic bearing as claimed in claim 1, comprising couNterbores tothe feed ducts in which the capillary tubes are welded into thecounterbores.
 5. A hydrostatic bearing as claimed in claim 1, comprisingcounterbores to the feed ducts in which the capillary tubes are brazedinto the counterbores.
 6. A hydrostatic bearing as claimed in claim 1,in the form of a radial bearing, in which the bearing unit has an outerface with a groove in the outer face constituting the common feedpassage, and comprising a ring forming the outer surface of the bearingand closing the said groove.
 7. A hydrostatic bearing as claimed inclaim 1, comprising a connection for connecting the common feed passageto an external pressure source, and a further connector connected to thecommon feed passage for drawing off liquid fed to the common feedpassage in excess of that required for feeding to the bearing pockets.8. A hydrostatic bearing as claimed in claim 7, in which the connectorand the further connector are arranged in opposition.
 9. A hydrostaticbearing as claimed in claim 7, comprising cooling passages in thebearing unit for carrying pressurized fluid.
 10. A hydrostatic bearingas claimed in claim 9, in which the cooling passages are connected inparallel with the common feed passage.
 11. A hydrostatic bearing asclaimed in claim 1, comprising a closable and externally accessibleconnector for each bearing pocket.